The present invention pertains to disc drives. More particularly, the present invention pertains to a removal system for removing a clamp from a hub in a disc drive.
A typical disc drive includes one or more magnetic discs mounted for rotation on a hub or spindle. Where more than one magnetic disc is used, the discs are spaced apart from one another axially along the hub by spacers mounted between the discs. Conventional hubs typically include a flange portion which extends from one of the axial ends of the hub. The discs and spacers are placed concentrically about the hub and supported by the flange portion of the hub. The plurality of magnetic discs and the spacers are clamped down onto the flange portion of the hub using a clamp which is placed on the axial end of the hub, opposite the flange. Thus, the discs and spacers are all clamped to the hub for rotation with the hub about an axis of rotation generally defined by the radial center of the hub.
A typical magnetic disc drive also includes a transducer supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducer and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from the host system. The drive controller controls the disc drive to retrieve information form the magnetic discs and to store information on the magnetic discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
Information is typically stored on the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data-from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is then decoded by the drive controller to recover the data represented by flux reversals stored on the magnetic disc, and consequently represented in the read signal provided by the data head.
As industry pressure requires disc drives to be reduced in size, the axial height of the hub, and consequently the axial height of the entire disc file, becomes critical. In past systems, the clamp used to hold the discs about the hub was screwed onto the hub with screws running in the axial direction. However, since the axial height of the hub has become critical, the screws used to fasten the clamp to the hub take up an undesirable amount of axial space.
Therefore, a heat shrink clamp was developed. Such a clamp is described in greater detail in U.S. Pat. No. 4,639,802. Such clamps typically include a clamp ring which has an inner diameter that is slightly smaller than the outer diameter of one axial end of the hub. The clamp ring is responsive to thermal energy and expands when thermal energy is applied to it and contracts when thermal energy is removed from it. Therefore, to assemble the clamp ring onto the hub, the clamp ring is first heated, thereby expanding it such that the inner diameter of the clamp ring is slightly larger than the outer diameter of the hub. The clamp ring is then placed about the hub and allowed to cool to establish a frictional or interference fit with the outer surface of the hub.
Just prior to placing the clamp on the hub, the plurality of discs and spacers arranged about the hub are subjected to an axial load. The clamp ring is put in place and allowed to form its frictional fit before the axial load is removed. Thus, the clamp ring clamps the spacers and the magnetic discs to the flange located at the second axial end of the hub.
At times, disc drives fail or need to be disassembled for inspection, or for other purposes. To remove thermally responsive clamps, a number of slots have traditionally been located in the first axial end of the hub about which the clamp is disposed. The slots communicate with the inner radial surface of the hub. A removal tool includes a number of fingers which corresponds to the number of slots in the hub. The fingers are positioned such that they mate with the slots in the first axial end of the hub, and a radial displacement is applied to the inner surface of the clamp by radially pivoting the fingers of the removal tool radially outward. This radial displacement is intended to enlarge the clamp so that its inner diameter is larger than the outer diameter of the hub, and so that the clamp can be removed.
However, in conventional removal systems, the number of slots in the hub, and consequently the number of corresponding fingers on the removal tool, is arbitrarily set at six. With only six slots and fingers, the performance of such a removal system is, at best, undesirable, and at worst, unacceptable, for many disc drives. With only six slots and fingers, the practical maximum attainable minimum radial expansion of the clamp is often less than the maximum radial interference between the inner surface of the clamp and the outer surface of the hub. The radial displacement also often induces large strains in the clamp.
Thus, with only six slots and fingers, there is a high degree of likelihood that the clamp will break during the removal process. When the clamp breaks, particles generated by the breakage disperse throughout the disc drive contaminating not only the data head assembly, but also the storage media. Such contaminated drives must be discarded as unusable.